Process for the preparation of aromatic esters



United States Patent US. Cl. 260-476 22v Claims ABSTRACT OF THEDISCLOSURE Process for preparing a carboxylic acid esters of a hydroxyaromatic, wherein the hydroxy group is on the aromatic nucleus, whichinvolves heating an aromatic hydrocarbon, a halogenated aromatichydrocarbon or an ester of an aromatic acid with iron, a noble metal orcompounds of iron or noble metal in the presence of a nitrate ion and acarboxylic acid.

This invention relates to a process for preparing a carboxylic acidester of a hydroxy aromatic, wherein said hydroxy group is on thearomatic nucleus, particularly to a process for preparing phenylacetate.

It is difficult to place oxygen on a nuclear carbon atom of an aromaticring. I have found that this can be done effectively under mildconditions, and a carboxylic acid ester of a hydroxy aromatic can beprepared, by the expedient of heating an aromatic compound with asubstance selected from the group consisting of iron, noble metals, ironcompounds and noble metal compounds in the presence of a substanceselected from the group consisting of nitrate ions and speciesconvertible to nitrate ions and a carboxylic acid. The present systemmust be essentially free of chloride or bromide ions. In the event aniron or noble metal chloride or bromide is employed herein, nuclearchlorination or bromination of the aromatic compound will occur, as setforth in my copending application Ser. No. 602,469 filed concurrentlyherewith. While this reaction is proceeding, the desired formation ofthe carboxylic acid ester of a hydroxy aromatic is not obtained.However, when the system becomes essentially free of chloride or bromideions, as evidenced by the formation of corresponding amounts ofhalogenated aromatics, the desired reaction defined 'herein will thenproceed.

The aromatic reactant employed herein can be an aromatic hydrocarbon, ahalogenated (chloro, bromo, fiuoro, or iodo) aromatic hydrocarbon or anester of an aromatic carboxylic acid wherein the alcoholic portion ofthe substituent thereof can be derived from methanol, ethanol and higherstraight and branched chain alcohols. Of these, methanol and ethanol arepreferred. Examples of aromatic compounds that can be employed hereininclude benzene, toluene, ethylbenzene, cumene, naphthalene, anthracene,biphenyl, phenanthrene, t-butylbenzene, u-phenylnaphthalene,para-xylene, polystyrene, terphenyl, 3-phenylheptane,1,4-diphenylbutane, diphenylmethane, tetralin, propylium anion, etc.

As noted, the second reactant employed herein can be iron, a noble metal(platinum, palladium, iridium, rhodium, osmium and ruthenium), ironcompounds and Patented Nov. 24, 1970 ice compounds of noble metals.Examples of iron compounds that can be employed include metallic iron,ferric acetate, ferric propionate, ferric hydroxy acetate, ferricchloride, ferric hydroxide, ferric nitate, ferric phosphate, ferricsulfate, ferrous acetate, ferrous nitrate, ferrous lactate, ferrousbromide, etc. Examples of noble metal compounds include palladium,rhodium, iridium, osmium, ruthenium, platinum, rhodium formate,palladium acetate, palladium propionate, iridium butyrate, palladiumpivalate, palladium octanoate, osmium isooctanoate, palladium benzoatepalladium laurate, ruthenium stearate, palladium isobutyrate, palladiumpara-toluate, platinum gammachlorobutyrate, ruthenium tetracontanoate,osmium phenylacetate, iridium cyclohexane carboxylate, rhodiumcrotonate, palladium furoate, palladium heptanoate, palladiumeicosanoate, palladium chloride, palladium nitrate, palladium oxide,rhodium bromide, iridium sulfate, osmium cyanide, ruthenium perchlorate,rhodium iodide, platinum fluoride, platinum phosphate, platinumpyrophosphate, ruthenium oxide, platinic bromide, platinous bromide,platinum oxide, platinous cyanide, platinum hydroxide, rhodium sulfate,rhodium oxide, osmium tetroxide, ruthenium trichloride, iridium oxide,etc.

Of the noble metal compounds that are employed herein I prefer acarboxylic acid salt of a noble metal. Thus, the cationic portion of thesalt can be one of the defined noble metals, preferably palladium, Whilethe anionic portion thereof can be derived from the group of carboxylicacids, straight and branched chain, having from one to 40 carbon atoms,preferably from two to six carbon atoms. Examples of such carboxylicacids are formic, acetic, propionic, butyric, pivalic, octanoic,isooctanoic, benzoic, lauric, stearic, isobutyric, para-toluic,gamma-chlorobutyric, tetracontanoic, phenylacetic, cyclo hexanecarboxylic, crotonic, furoic, heptanoic, eicosanoic, etc. Examples ofcarboxylic acid salts of noble metals that can be employed includerhodium formate, palladium acetate, palladium propionate, iridiumbutyrate, palladium pivalate, palladium octanoate, osmium isooctanoate,palladium benzoate, palladium laurate, ruthenium stearate, palladiumisobutyrate, palladium para-toluate, platinum gamma-chlorobutyrate,ruthenium tetracontanoate, osmium phenylacetate, iridium cyclohexanecarboxylate, rhodium crotonate, palladium furoate, palladium heptanoate,palladium eicosanoate, etc.

In order to obtain the desired reaction herein with substantialproduction of the desired carboxylic acid ester of a hydroxy aromatic itis imperative that the above reactants be brought into contact with eachother in the presence of a substance selected from the group consistingof nitrate ions and species convertible to nitrate ions. By nitrate ionsI mean N0 1 a singly charged anion containing one nitrogen atom andthree oxygen atoms. By species convertible to nitrate ions I mean toinclude compounds, ions or radicals containing nitrogen and oxygen whichby ionization, oxidation or disproportionation under conditions definedfor this process give NO Species convertible to nitrate ions that can beemployed herein include nitric acid, nitric oxide, nitrous anhydride,nitrate ion, nitrous acid, nitrogen dioxide, nitrogen tetroxide, nitricanhydride, etc.

Also required in the reaction system is a carboxylic acid, examples ofwhich have been defined above. The

amount of carboxylic acid employed, relative to the iron or noble metalcatalyst, on a weight basis, can be from about 10 :1 to 1:1, preferablyfrom about 10 :1 to 100:1.

Preferably, the aromatic compound, the iron or noble metal species, thecarboxylic acid and the nitrate ion are heated in the presence of asolvent which will not ad versely affect the course of the reaction andwill not react with the reactants and/ or the products produced herein.Examples of such solvents are ethers, amides, s'ulfoxides, ketones, suchas meta dioxane, dimethylacetamide, dimethylformamide,dimethylsulfoxide, acetone, etc. In a preferred embodiment, however, thesolvent can be the carboxylic acid, straight and branched chain havingfrom one to 40 carbon atoms, preferably from two to six carbon atoms,specific examples of which have been set forth above.

The reaction defined herein is simply effected by bringing the materialsdefined above into contact with each other under specified conditions.The amount of aromatic to iron, noble metal or compounds thereof, asmetal, on a molar basis, employed can range from about 1:1 to about 10:1, preferably from about 10:1 to about 10 :1. The amount of nitrate ionemployed, on a molar basis, relative to the aromatic compound, can befrom about 1:1 to about 1:10, preferably from about '1:3 to about 1:10The amount of solvent employed can be from about 0.1 to about 1000 mols,preferably from about 1 to about 50 mols, per mol of aromatic compound.The temperature employed during the process can range from about 40 toabout 200 C., preferably from about 60 to about 150 C., the pressurefrom about 0.1 to about 10,000 pounds per square inch gauge, preferablyfrom about to about 1000 pounds per square inch gauge, and the contacttime from about 0.1 to about 100, preferably from about one to about 10hours.

At the end of the reaction period, iron or noble metal may precipitateout of solution and can be recovered thereof in any convenient manner,for example, by distillation and removal of the organic portions of theproduct. During the distillation unreacted hydrocarbon, carboxylic acidand solvent will come off before the product and can be isolated in apure form thereby and recycled and will be followed in the distillationby the carboxylic acid ester of the hydroxy aromatic. The temperature,pressure and reflux ratio necessary to carry out the distillation willdepend on the components involved and are readily determinable by thoseskilled in the art. If desired to reemploy the metal so recovered in theform of a compound, for example, the salt thereof, the metal can beheated wtih a carboxylic acid, such as defined hereinabove, in amolecular oxygen atmosphere to convert the metal to a metal carboxylate.This is believed to require the use of one mol of metal, two mols ofcarboxylic acid and one-half mol of molecular oxygen, resulting in theproduction of one mol of the metal carboxylate and one mol of water.This oxidation procedure can involve a temperature of about 80 to about180 C., a pressure of about 50 to about 3000 pounds per square inchgauge and a reaction time of about 0.1 to about 100 hours. Compoundsresulting from the process defined herein include phenyl acetate, phenylfuroate, a-naphthyl acetate, fl-naphthyl propionate, Z-anthracylbutyrate, para-phenylpheuyl isoctanoate, 9-phenanthryl tetracontanoate,para-t-butylphenyl laurate, para-pivaloxychlorobenzene, methylmetaacetoxybenzoate, 4-chloro-4'-phenylacetoxybiphenyl,1-phenyl-4-para-toluoxynaphthalene, Z-(meta-acetoxyphenyl)thiophene,S-acetoxy benzofuran, para-tolyl acetate, meta tolyl acetate, orthotolyl acetate, para-ethylphenyl acetate, 3-(para-butyroxyphenyl)heptane,1-(para-acetoxyphenyl-4-phenylbutane, 5-actoxy-1,2,3,4-tetrahydronaphthalene, etc.

The process of the invention can further be illustrated by thefollowing.

EXAMPLE I There was refluxed at atmospheric pressure and a refluxtemperature of 115 C. over a period of 23 hours a mixture of 20millimols of an aromatic compound, 1.0 millimol of palladium acetate, 10millimols of sodium acetate, 0.5 millimol of percent aqueous nitric acidand 25 milliliters of acetic acid. At the end of the reaction period thereaction mixture was analyzed by gaslbiqluid chromatography. The resultsobtained are analyzed e ow.

and Z-naphthyl acetate.

The results from Runs Nos. 1, 2, 3 and 5 show that aromatic compoundsnot encompassed within the definition of aromatic compounds definedherein cannot be employed herein to obtain the defined products.

EXAMPLE II In a series of similar runs various Group VIII metals wereexamined as to their ability to catalyze the desired acetoxylation ofbenzene. In these runs a mixture of 1.0 milligram atom of each metal wasstirred in 25 milliliters of acetic acid containing 20 millimols ofbenzene and 70 percent aqueous nitric acid at atmospheric pressure andreflux temperature. The reaction product was analyzed by gas-liquidchromatography. As the results in Table II show the noble metals andirons were eflective but nickel was an ineflective catalyst.

TABLE II Nitric Phenyl Time, acid acetate, Run number hours Metalmlllimols millimol 7 6 Platinum- 1. 0 O. 13 22 ,.do l. 0 0.42 8 6Palladium 1. 0 1. 43 22 .do 1.0 1.42 9 6 Iridium.-- 1.0 0.42 22 do 1. 01.30 10 6 Ruthenium.-. 1. 0 0. 50 22 -do 1.0 1.37 1. 0 0. 69 1. 0 1. 233. 0 0. 7 3. 0 2. 0 3. 0 0 Ruthenium--. 3. 0 l. 5

EXAMPLE III An additional series of runs were made in which 50milliliters of a solution containing 50 percent by weight of benzene and50 percent by weight of acetic acid, various amounts of nitric acid andvarious amounts of palladium were refluxed at atmospheric pressure andC., stirred and analyzed by gas-liquid chromatography. It can be seenfrom Table III below that up to 290 mols of phenyl acetate are formedper mol of palladium, indicating that palladium serves as a catalystherein.

TABLEIIII 6 palladium acetate and five millimols of salt. Afterreiluxing for 24 hours at atmospheric pressure and a temperature of 85C. each system was analyzed by gas chro- Palladium Time, hours Runnumber Type Nitric acid, Millimols millimols Mols phenyl acetate formedper mo palladium EXAMPLE IV That a nitrate ion or a species convertibleto a nitrate ion is required is illustrated by the following. There wasrefluxed at atmospheric pressure and at a temperature of 115 C. 20millimols of benzene, palladium acetate and matography, five millimolsof nitric acid was added and after an additional 68 hours of refluxanalyzed again. A comparison of the product before and after nitric acidaddition shows a significant improvement in the amount of phenyl acetateobtained. The results are tabulated below in Table V.

TABLE V After 24 hours of reflux .but before nitric acid addition 68hours of reflux after addition of nitric acid Phenyl acetate, Biphenyl,Phenyl acetate, Biphenyl, Nitro benzene, Run number Salt weight percentweight percent weight percent weight percent weight percent 33 NazSO; 0.14 0.22 1. 29 0. 30 0. 20 34. 3F 0. 03 0.15 0. 43 0. 25 35- KCN 0 0 1.50 0 0 36 LiClO4 0.02 0. 23 0.46 0.50 0.15 37 NaI 0 0 0.54 0 0 3s NaHPOi0.01 0. 08 0.28 0.18 0

25 millimols of acetic acid. The reaction product was analyzed bygas-liquid chromatography. The results are tabulated below in Table IV.

EXAMPLE VII A mixture of 1.15 grams of palladium nitrate, five millimolsof toluene and 20 milliliters of acetic acid were TABLE IV Results basedon palladium, yield of- Run acetate, Benzene, time, Phenyl numberAdditive Millimols millimols millimols hours acetate Biphenyl Silveracetate 5 24 4 16 23 Dimethylacetamid 140 5 57 64 4 1. 5 24 Sulfuricacid. 10 5 86 88 0 58 25--. Magnesium perchlorate 2 2 8 2O 0 20 26Ammonium acetate 5 20 20 0 0 27 Triphenyl phosphine. 10 5 20 20 0 1 28Triphenylamine 10 5 20 20 0 0 29 Water 12 5 2 201 4 8 30.. Ammoniumsulfate 20 5 20 20 0 0 31 None. 5 2O 20 6 10 32 Nitric acid 5 20 20 48 4EXAMPLE V refluxed for 20 hours at atmospheric pressure and 116 C.

EXAMPLE VI Into SO-milliliter flasks were placed 25 milliliters of asolution consisting of 50 percent by weight of benzene and 50 percent byweight of acetlc acid, one millimol of Analysis by gas chromatography ofthe product in this run (Run No. 39) showed the yield of acetoxylatedtoluene was 60 percent and this consisted of 11.9 percent meta tolylacetate, 14.4 percent para tolyl acetate, 15.4 percent ortho tolylacetate and 58.3 percent benzyl acetate. Small amounts ofp,p'-dimethylbiphenyl and other toluene dimers were also formed.

EXAMPLE VIII In this run (Run N0. 40) a mixture of 1.58 grams ofbenzene, 0.2317 grams of palladium acetate, 25 milliliters of propionicacid and one millimol of nitric acid was refluxed for 20 hours. Analysisof the product by gas chromatography disclosed 0.76 millimols of phenylpropionate.

EXAMPLE IX The present run (Run No. 41) involved heating at atmosphericpressure and 115 C. over a period of 68 hours a mixture of 25milliliters of acetic acid, 20 millimols of benzene, one millimol ofsodium nitrate and one millimol of palladium acetate. Analysis by gaschromatography showed the presence in the mixture of 0.1 percent byweight of phenol and 0.1 percent by Weight of phenyl acetate. The phenolresulted from hydrolysis of phenyl acetate.

EXAMPLE X The present run (Run No. 42) discloses that cobalt and nickelis inoperative herein. A 25 milliliter solution of 20 millimols ofbenzene in acetic acid, three millimols of nitric acid and one millimolof cobalt metal was refluxed for 68 hours at atmospheric pressure and115 C. No phenyl acetate was found. An additional experiment similar tothe above was conducted in which one millimol of nickel metal wasemployed in place of cobalt. Again no phenyl acetate was found.

Obviously, many modifications and variations of the invention, ashereinabove set forth, can be made without departing from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims.

I claim:

1. In a process for preparing a carboxylic acid ester of a hydroxyaromatic, said hydroxy group being on the aromatic nucleus, wherein anaromatic compound selected from the group consisting of an aromatichydrocarbon having from six to 16 carbon atoms and at least one hydrogenon a ring thereof, a halogenated aromatic hydrocarbon having from six to16 carbon atoms and at least one hydrogen on a ring thereof and an alkylester of an aromatic hydrocarbon carboxylic acid having from six to 16carbon atoms and at least one hydrogen on a ring thereof, wherein thecarboxylic acid group of said ester is on a ring thereof and the alkylportion of said ester is derived from a lower alcohol, is heated with alower carboxylic acid and a metalic compound selected from the groupconsisting of iron, a noble metal selected from the group consisting ofplatinum, palladium, iridium, rhodium, osmium and ruthenium andcompounds of iron and said noble metals, the improvement which comprisesadditionally having present a substance selected from the groupconsisting of nitrate ions and species convertible to nitrate ions.

2. The process of claim 1 wherein the reactant aromatic compound is saidaromatic hydrocarbon.

3. The process of claim 1 wherein reactant aromatic compound is saidhalogenated aromatic hydrocarbon.

4. The process of claim 1 wherein the reactant aromatic compound is saidester of an aromatic hydrocarbon carboxylic acid.

5. The process of claim 1 wherein the reactant aromatic compound isbenzene.

6. The process of claim 1 wherein the reactant aromatic compound isnaphthalene.

7. The process of claim 1 wherein the reactant aromatic compound ismethyl benzoate.

8. The process of claim 1 wherein said metallic compound is a salt of anoble metal.

9. The process of claim 1 wherein said metallic compound is a carboxylicacid salt of a noble metal.

10. The process of claim 1 wherein said metallic compound is iron.

11. The process of claim 1 wherein said metallic compound is platinum.

12. The process of claim 1 wherein said metallic compound is palladium.

13. The process of claim 1 wherein said metallic compound is iridium.

14. The process of claim 1 wherein said metallic compound is ruthenium.

15. The process of claim 1 wherein said metallic compound is rhodium.

16. The process of claim 1 wherein said metallic compound is palladiumacetate.

17. The process of claim 1 wherein said metallic compound is palladiumchloride.

18. The process of claim 1 wherein said metallic compound is palladiumnitrate.

19. The process of claim 1 wherein the reaction is carried out in thepresence of a species convertible to nitrate ions.

20. The process of claim 1 wherein the reaction is carried out in thepresence of nitric acid.

21. The process of claim 1 wherein the reaction is carried out in aninert solvent.

22. The process of claim 1 wherein the reaction is carried out at atemperature of about 40 to about 200 C., a pressure of about 0.1 toabout 10,000 pounds per square inch gauge and a contact time of about0.1 to about hours.

References Cited UNITED STATES PATENTS 3,418,361 12/1968 Kaeding et al.260473 JAMES A. PATTEN, Primary Examiner D. E. STENZEL, AssistantExaminer US. Cl. X.R.

